"We already know from other studies that work-related stress is associated with many adverse health outcomes, such as heart disease and depression," said lead researcher Katriina Heikkila, from the Finnish Institute of Occupational Health in Helsinki.

"Our findings suggest that stress at work is unlikely to be an important cancer risk factor. Though reducing work stress would undoubtedly improve the psychological and physical well-being of the working people, it is unlikely to have a marked impact on cancer," Heikkila said.

Commenting on the new report, Dr. Lidia Schapira, associate editor for psychosocial oncology at the American Society of Clinical Oncology's Cancer.Net, said, "I am encouraged that there is now some evidence that uncouples job strain and life stresses from cancer."

People worry a lot when they are under stress, and they then worry that their worrying is going to impact their health, she noted.

"We know stress can affect the body's reactions [and] increase inflammation, which is associated with an increased risk of cancer, so there is good reason to worry," said Schapira, who is also an assistant professor in the department of medicine at Harvard Medical School in Boston.

"I think people should address stress just because stress is uncomfortable and impacts on one's wellness and well-being and quality of life," Schapira said. "But good scientists have given it a hard look, and we really can't connect the dots [between] being stressed at work to getting cancer."

The analysis was published online Feb. 7 in the BMJ.

To see what role job stress might play in the risk of developing cancer, Heikkila's group collected data on 116,000 men and women, aged 17 to 70, from Finland, France, the Netherlands, Sweden, Denmark and the United Kingdom.

All of these people had taken part in one of 12 studies where they were asked about the amount of stress on their job.

The researchers defined several types of job stress: high-stress jobs, with high work demands and low control over work; active jobs, with high demands and high control; passive jobs, with low demands and low control; and low stress jobs, with low demands and high control.

The investigators then turned to cancer death registries and hospital records to see how many people developed or died from cancer. They further refined their search by taking age, sex, socioeconomic factors, smoking and alcohol use into account.

In addition, the researchers excluded anyone who was extremely overweight or underweight.

Over an average 12 years of follow-up, more than 5,700 people developed some type of cancer.

Heikkila's team didn't find any connection, however, between cancer and job stress. It is possible that other studies that found a connection between job stress and cancer found the association by chance or included other work-related factors that went beyond work, the Finnish researchers said.

For this type of study, called a meta-analysis, researchers comb through already published studies looking for patterns in the data. Often, the patterns they find go beyond the original intent of the studies they are examining.

The downside of a meta-analysis is that the data the researchers choose is only as good as the data in the studies they use, and their conclusions can't always take into account problems with the original research.

Elizabeth Ward, national vice president of intramural research at the American Cancer Society, said it is hard to conclude from this analysis that work stress doesn't play a role in cancer.

"One way job stress could impact cancer is if people who have stress are more prone to be smokers or drink more alcohol, or be obese," she explained.

When the researchers tried to eliminate these factors from their data, they could be hiding a substantial number of people for whom stress leads directly to behaviors known to increase the risk for cancer, Ward noted.